In the aforenoted patents, it was explained that the conventional double-pointed cannula as used with conventional evacuated containers gave rise to problems of possible contamination, piercing of the fingers of the operators, clotting of the inner tip during the interchange of containers and extravasation of blood from an adjacent vein and hematoma if the outer tip of the double-ended cannula lodges within tissues rather than a vein.
In the earlier embodiments of the device to be described herein, these difficulties were avoided through a construction in which the cannula-containing portion of the device and the container each included a valve. In particular, the container portion included a valve which could be opened gradually, presenting the advantage that should the flow of blood not start almost immediately after cracking the valve, the valve could be shut. This feature provided the advantage of indicating that the needle had not been placed correctly into a vein, thereby alerting the operator to the need for removing the needle and re-inserting same.
Although the earlier embodiments of the present invention successfully overcame the aforenoted disadvantages, it was found that the device was somewhat complex both as to structure and as to method of use, making the device relatively expensive and requiring training of the operator. Accordingly, it became evident that it would be desirable to simplify the construction of the device from the standpoint of operation as well as from the standpoint of cost.